A vacuum tube, electron tube, valve, or tube, is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.
Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. HVAC system design is a subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer. "Refrigeration" is sometimes added to the field's abbreviation as HVAC&R or HVACR, or "ventilation" is dropped, as in HACR.
A furnace, referred to as a heater or boiler in British English, is an appliance used to generate heat for all or part of a building. Furnaces are mostly used as a major component of a central heating system. Furnaces are permanently installed to provide heat to an interior space through intermediary fluid movement, which may be air, steam, or hot water. Heating appliances that use steam or hot water as the fluid are normally referred to as a residential steam boilers or residential hot water boilers. The most common fuel source for modern furnaces in North America and much of Europe is natural gas; other common fuel sources include LPG, fuel oil, wood and in rare cases coal. In some areas electrical resistance heating is used, especially where the cost of electricity is low or the primary purpose is for air conditioning. Modern high-efficiency furnaces can be up to 98% efficient and operate without a chimney, with a typical gas furnace being about 80% efficient. Waste gas and heat are mechanically ventilated through either metal flue pipes or polyvinyl chloride (PVC) pipes that can be vented through the side or roof of the structure. Fuel efficiency in a gas furnace is measured in AFUE.
A thermostat is a regulating device component which senses the temperature of a physical system and performs actions so that the system's temperature is maintained near a desired setpoint.
Water heating is a heat transfer process that uses an energy source to heat water above its initial temperature. Typical domestic uses of hot water include cooking, cleaning, bathing, and space heating. In industry, hot water and water heated to steam have many uses.
A central heating system provides warmth to a number of spaces within a building from one main source of heat. It is a component of heating, ventilation, and air conditioning systems, which can both cool and warm interior spaces.
A storage heater or heat bank (Australia) is an electrical heater which stores thermal energy during the evening, or at night when electricity is available at lower cost, and releases the heat during the day as required. Alternatively, solar storage heaters are designed to store solar energy as heat, to be released during the night or other periods where it is required, often making it more cost effective than selling surplus electricity to the grid and buying it back at night.
A heating element converts electrical energy into heat through the process of Joule heating. Electric current running through the element encounters resistance, resulting in heating of the element. Unlike the Peltier effect, this process is independent of the direction of current.
A pilot light is a small gas flame, usually natural gas or liquefied petroleum gas, which serves as an ignition source for a more powerful gas burner. Originally a pilot light was kept permanently alight, but this wastes gas. Now it is more common to light a burner electrically, but gas pilot lights are still used when a high energy ignition source is necessary, as in when lighting a large burner.
A smudge pot is an oil-burning device used to prevent frost on fruit trees. Usually a smudge pot has a large round base with a chimney coming out of the middle of the base. The smudge pot is placed between trees in an orchard. The burning oil creates heat, smoke, carbon dioxide, and water vapor. It was believed that this oil burning heater would help keep the orchard from cooling too much during the cold snaps.
Superinsulation is an approach to building design, construction, and retrofitting that dramatically reduces heat loss by using much higher insulation levels and airtightness than average. Superinsulation is one of the ancestors of the passive house approach.
Electric heating is a process in which electrical energy is converted directly to heat energy. Common applications include space heating, cooking, water heating and industrial processes. An electric heater is an electrical device that converts an electric current into heat. The heating element inside every electric heater is an electrical resistor, and works on the principle of Joule heating: an electric current passing through a resistor will convert that electrical energy into heat energy. Most modern electric heating devices use nichrome wire as the active element; the heating element, depicted on the right, uses nichrome wire supported by ceramic insulators.
A fan heater, also called a blow heater, is a heater that works by using a fan to pass air over a heat source. This heats up the air, which then leaves the heater, warming up the surrounding room. They can heat an enclosed space such as a room faster than a heater without a fan, but like any fan, create a degree of noise.
An electric blanket is a blanket that contains integrated electrical heating wires. Types include underblankets, overblankets, throws, and duvets. An electric underblanket is placed above the mattress and below the bottom bed sheet. This is the most common type in the UK and Commonwealth countries, where it is known by default as an "electric blanket"; in the U.S. and Canada, where it is less common, it is called an electric heated mattress pad. An electric overblanket is placed above the top bed sheet, and is the most common type in the U.S. and Canada, where it is called an "electric blanket".
A space heater is a device used to heat a single, small- to medium-sized area. This type of heater can be contrasted with central heating, which distributes heat to multiple areas.
A convection heater is a heater that uses convection currents to heat and circulate air. These currents circulate throughout the body of the appliance and across its heating element. This process, following the principle of thermal conduction, heats the air, reducing its density relative to colder air and causing it to rise.
An oil burner is a heating device which burns #1, #2 and #6 heating oils, diesel fuel or other similar fuels. In the United States ultra low #2 diesel is the common fuel used. It is dyed red to show that it is road-tax exempt. In most markets of the United States heating oil is the same specification of fuel as on-road un-dyed diesel.
An electric fireplace is an electric heater that mimics a fireplace burning coal, wood, or natural gas. Electric fireplaces are often placed in conventional fireplaces, which can then no longer be used for conventional fires. They plug into the wall, and can run on a "flame only" setting, or can be used as a heater, typically consuming 1.4 to 1.6 kW to heat a 40 m2 room.
A heater is an appliance whose purpose is to generate heat for a building.
Radiators and convectors are heat exchangers designed to transfer thermal energy from one medium to another for the purpose of space heating.
